Yesterday I was out in my shop with some oven cleaner to remove some build up on my saw blades. When I was finished I sprayed some of the oven cleaner on a piece of QS White Oak and was amazed at how fast I got the same results of popping the grain of my sample piece. I’ve fumed before on several projects and really like the results, but it takes time and a chamber and a lot of care. I understand that what makes this process work is the interaction between the ammonia and the presence of tannin in the wood, but why do we have to fume to get this result? If simply using either a low strength liquid ammonia or even the oven cleaner directly on the piece gets the result you want, why not go that route? Am I missing something here? The oven cleaner darkend the test piece in five minutes and that would have taken 30+ hours in a chamber.
dg
Replies
No you are not missing anything folks have been using a very dilute lye solution for darkening oak for years.I just use a plant spray.BE VERY CAREFUL of your eyes as it dissolves mother -in -laws and damages eyes
Is there any difference in the color tone using the diluted lye? Just how do you know about the mother in law thing?
dgDave Graf
I have found that About !/2 to 3/4 tsp in a quart of water works well and just apply several times to darken.It does raise the grain so experiment.Just be careful as I have read that strong alkali is more damaging to the cornea than acid.I have only finished work with pre-cat which after 5 yrs was still ok
Edited 1/25/2008 11:40 pm ET by jako17
I thought that a bucket of water was the preferred weapon against unwanted females.......Best,JohnWho feeds the flying monkeys once she's gone?
Edited 1/25/2008 1:42 pm ET by Jmartinsky
It is the lye not ammonia that is the secret of the oven cleaners dramatic success. Sadly, the same ingredient is also so severely caustic that it must be THOROUGHLY NEUTRALIZED if one hopes to eliminate the hazards of chemical action eating the finish over time. This thorough neutralization process has the significant drawback of also reversing the effects of the treatment... so here we are back at square one with our wood well scrubbed and hopefully not TOO contaminated and looking very much the same as it did to begin with. Hopefully we only spent half a day or so in this learning process and now we are beginning to understand WHY WE FUME!!!
I'm not the chemist, but here are some comments, an important difference has been mentioned already, oven cleaner contains sodium hydroxide (NaOH), not ammonium hydroxide (NH4OH) that is used for fuming. The reason why oven cleaner also darkens wood is because sodium hydroxide oxidizes tannins. It is correct to fume with ammonium hydroxide and not to apply it directly to the wood because the fumes created by it is ammonia gas (NH3) that produces the oxidation of tannins. If we apply the ammonium hydroxide directly onto the wood it oxidizes tannins but the topcoat finish will react with the hydroxide as it is a strong base. There will be a strong reaction with any acid compound on the topcoat we use as well as a strong reaction with latex products (independent of acidity), strong reaction with chloride containing compounds, metals used as driers, and many other reactions. There are other many other oxidizing agents that have been used to react with tannins.
Wood tannins are complex molecules and not all plants produce the same molecule, the same wood species may give different color when tannins are oxidized, we may not expect the same color to develop each time we repeat the process even if it is the same type of wood. Eddit add: the more concentrated the ammonium hydroxide, the more ammonia gas formed, the faster the reaction, that is why cleaning ammonia is not as effective or as fast as concentrate "industrial" ammonia.
Edited 1/25/2008 10:50 pm ET by woodshaves
Can the same results as fuming/oven cleaner be achieved with aniline dyes/pigment stains/topcoat? Without the very serious problems of ammonia/lye, etc.
I seem to recall an article in FWW that described the process.
I also recall a Knots thread that said oven cleaner (lye) is very detrimental to the welds that hold the saw teeth to the plate.
I need to learn how to index/retrieve these nuggets of wisdom.
Pete
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